Rough Riders are one of the fast moving units in the Imperial Guard armies, they are well known for their mobility and epic charges that make the best horse riders of the middle ages jealous, their role is fast hit-and-run assaults or scouting ahead of the main force. Their spears are tipped with a number of stuff to deal with the many threats they face in combat. it is a truly awesome sight to see them charge through waves of Orks, clashing quickly with their foe before firing their explosive-tipped spears at their armor and heavy troops. Here is a fan animation for visual proof.
The Rough Riders can be seen mounted on many fast moving life forms like big horses, big cyber-horses, cyber-mutated-beast-horse-thingys, Dinosaurs, and many other creatures... when they operate far from supply lines they can drink some of their mounts' blood so as not to die from thirst...(actually Mongols did this back then, which was justified due to the fact that their horses were as hardcore as they themselves. The Hung from Fantasy do this too, since they were inspired by the Mongols.) Although this makes you wonder about the cyborg Deathriders, who probably have motor oil for blood. Overall, they are, despite being largely ignored by GW and fanbase (since their spears are one-use only, which makes them quite useless in play), one of the coolest units in Warhammer 40k, what's not cool about a badass motherfucker riding a big badass cyber-horse?
The original "Attilan" Rough Rider models haven't been updated since 2nd edition, and consequently, look ugly as fuck compared to everything else in the Imperial Guard codex (except Catachans). Thankfully Perry Miniatures makes 28mm plastic cavalry, Civil War Cavalry & British Hussars blend very well with Praetorian, Mordian, Valhallan, and Vostroyan regiments, although you could always justify them as just being ceremonial (aka fancy) Guardsmen. Oh, and the best part? You get 14 of these guys for only $36. Just glue a bayonet to the end of a toothpick and you've got a hunting lance!
And here's an example of a mutated horse thing that the Death Korps of Krieg mount.
arabicTallarn rough rider.